This invention relates to a compressed air system, and specifically an air dryer assembly for the compressed air system that removes moisture and oil. The invention finds particular application in a compressor system for vehicles that use pressurized air to selectively control application of vehicle brakes and for other air operated systems associated with the vehicle.
Compressed air systems are used in conventional brake systems, for example, to provide and maintain air under pressure to operate vehicle brakes and auxiliary air systems. Water, particulates, and oil in the compressed air system can lead to component degradation and interfere with optimal operation of the system. Accordingly, an air dryer is usually incorporated into the system to remove water from the compressed air. The air dryer collects and removes air system contaminants in solid, liquid, and vapor form before the contaminants enter the system. The air dryer delivers clean, dry air for braking system components, thereby increasing system life and reducing maintenance costs.
An air brake compressor is typically supplied with oil from the vehicle engine in order to lubricate bearings and other components of the compressor. As will be appreciated, it is difficult to contain the oil in the compressor and oil occasionally becomes entrained in the pressurized air stream exiting the compressor. Modern air dryers use a desiccant material to adsorb water vapor as it passes through an air line from the compressor toward a reservoir or downstream components. The operation and efficiency of the desiccant is adversely affected by oil and thus it is important to minimize contamination of the desiccant with oil by employing a filtering element or oil filter that effectively removes the oil.
In addition, commercially available desiccant-type air dryers provide a structure that allows for replacement of the desiccant material. Periodic replacement of the desiccant material is desirable since, in use, the desiccant material becomes coated with contaminants such as oil, which ultimately reduces its water vapor retention characteristics. Since other components of air dryers have a longer service life, a convenient system for selectively replacing the desiccant material is desired. For example, a spin-on type desiccant air dryer cartridge resembles a conventional motor vehicle spin-on oil filter in the form of a canister. A load plate has a centrally threaded bore such that the entire replaceable air cartridge unit is threaded onto an upstanding boss extending from a mounting surface of the vehicle.
An oil coalescing element removes a majority of aerosols and liquid oil entering a spin-on desiccant cartridge. Unfortunately, known designs have not adequately addressed removal of coalesced oil from the cartridge. For example, purge flow systems direct air flow in a reverse direction or back through the oil coalescing element in an effort to remove entrained oil from the desiccant. However, a poor design can lead to desiccant leakage, to a reduction in the removal of oil from the cartridge, thus leading to a decrease in desiccant life, and ultimately to a negative impact on the performance of the compressed air system.
Thus, a continued need exists in the art to effectively eliminate desiccant contaminant in an air dryer assembly of a compressed air system, to remove the contaminant from the dryer assembly, and to contain the desiccant.